There are phenomena in which interaction between bodies is so fast that it is difficult to measure the forces that are produced between them or the time that the interaction lasts.

   For example, how long does the collision between two billiard balls last for? What force does one ball apply on the other? These questions are, no doubt, difficult to answer. Should we give up trying to calculate the result of collisions? Should we leave everything to the billiard player's experience and intuition?

   No, physics doesn't give up on trying to explain phenomena that look difficult that easily.

   In these cases, the notion of linear momentum and impulse, in addition to the conditions under which linear momentum is conserved, will allow us to make predictions of the speed and direction of the movement after the interaction.